To set an interim plan for selected tasks, in the desired project, select the desired tasks (using the Shift or Ctrl keys), then go to menu Project – Set Baseline. Check the Set interim plan option – select the desired field from the Copy drop down menu – select the desired field from the Into drop down menu – select the Selected Tasks option then click OK. The fields selected from the Into dropdown will contain the values from the Copy dropdown.
Note: If the selected fields are StartX/FinishX, then only the Start/Finish values will be copied. If the fields are Baseline, then all the values for the baseline fields will be copied.